A study on the mechanical polishing technique by using shear thickening fluids

This paper reported the new polishing technique by using a shear thickening fluid (STF). In experiments, the steel workpiece was immersed into the STF under the static condition. When the workpiece started rotating at a certain speed, the surrounding STF became solidified due to the shear thickening effect. Consequently, the solidified STF held the abrasive particles and polished the surfaces of the workpiece. The surface roughness of the treated surfaces was clearly dependent on the size of the abrasive particles. Owing to the reversible phase transition between liquid and solid status for the STF, the polishing process can be conducted without the use of polishing pads. Moreover, the new polishing technique using the STF can polish some complex structures having the surfaces with different heights and/or orientations, which cannot be achieved by the traditional one-step polishing method.

In-situ ellipsometry measurements on the phase segregation of mixed halide lead perovskites

Mixed halide lead perovskite such as methylammonium lead iodide bromides MAPb(BrxI1-x)3 have emerged as one of the most promising materials of future solar cells, offering high power conversion efficiencies and bandgap tunability. Among other factors, the reversible phase segregation under even low light intensities is still limiting their potential use. During this process, the material segregates locally into iodide-rich and bromide-rich phases, lowering the effective bandgap energy. While several studies have been done to illuminate the mechanism and suppression of phase segregation, fundamental aspects remain unclear. Phase compositions after segregation vary extensively between different studies and the exact amounts of phases often remain unmentioned. For iodide-rich phases, the end-point compositions at around x=0.2 are widely accepted but the proportion of the phase is difficult to measure. In this report, we observe the phase segregation using spectroscopic ellipsometry, a powerful, nondestructive technique that has been employed in the study of film degradation before. We obtained dynamic ellipsometric measurements from x=0.5 mixed halide lead perovskite thin films protected by a polystyrene layer under green laser light with a power density of ~11 W/cm2. Changes in the bandgap region can be correlated to the changes in composition caused by phase segregation, allowing for the kinetics to be observed. Time constants between 1.7(± 0.7)×10-3 s-1 for the segregation and 1.5(± 0.6)×10-4 s-1 for recovery were calculated. We expect ellipsometry to serve as a complementary technique to other spectroscopies in studying mixed-halide lead perovskites phase segregation in the future.

Effect of off-stoichiometry on the thermal conductivity of amorphous GeTe

The reversible phase change of Germanium Telluride (GeTe) is essential for developing advanced non-volatile devices. We investigate off-stoichiometric effect on the thermal and structural properties of amorphous Ge$_{1-\delta}$Te (0 $\le$ $\delta$ $\le$ 0.12) via molecular dynamics. The structural optimization due to off-stoichiometry was taken into account with an empirical potential. Our simulated thermal conductivity is in the range of experimental observations. With increasing $\delta$, the thermal conductivity tends to be slightly reduced. Analysis on the coordinate number and the bond angle distribution indicates that the off-stoichiometric Ge$_{1-\delta}$Te still retain its ability of rapid phase transition. These results are helpful in reliable device design and modeling.

Synthesis, crystal structure, and thermal stability of double borate Na3ErB2O6

Double borate Na3ErB2O6 was synthesized by the solid-state reaction. The crystal structure of Na3ErB2O6 was refined by the Rietveld method: P21/c, a = 6.49775(14) Å, b = 8.50424(17) Å, c = 12.0067(3) Å, β = 118.4797(9)°, Z = 4. The crystal structure of Na3ErB2O6 consists of –[ErO6]∞-chains along the "b" axis, which are linked by BO3 triangles in a three-dimensional framework. Sodium atoms occupy empty positions inside the channels. The thermal behavior of Na3ErB2O6 was studied in detail in the range of 25–1150 °C range by DSC and TG methods. Na3ErB2O6 congruently melts at 1116 °C. Based on the results of DSC measurements, three reversible phase transitions were found for Na3ErB2O6.